1. Field of the Invention
The present invention relates to an electronic apparatus, and more particularly, to an electronic apparatus that discharges hot air generated by a heat element to the outside of a casing thereof.
2. Description of the Related Art
There have been conventionally known a structure of a casing that discharges heat generated by a heat element in the casing, and a heat sink. In the heat sink, there have been known a structure to enlarge a volume or a surface area in order to improve a heat radiation effect, and a structure to make a surface, which should be contacted to the casing, plane in order to make the surface come in contact with the casing closely.
As such a structure, for example, Japanese Patent Application Publication No. 2004-349560 (Document 1) discloses a cooling electronic apparatus in which heat parts are thermally connected to an inside surface of a wall portion of a casing which composes the cooling electronic apparatus, and an air hole is provided at the wall portion of the casing in the vicinity of the heat parts.
In Japanese Patent Application Publication No. 2001-291806 (Document 2), there has been known a technique that discharges heat generated by a CPU to the outside of a note-type personal computer by attaching an end of a heat sink to a surface of the CPU in the note-type personal computer. A plurality of heat radiation grooves are formed on the heat sink in parallel along the direction of the heat radiation.
However, in the cooling electronic apparatus of Document 1, the air hole is provided at a bottom portion of the casing. The air (i.e., the hot air) warmed with the heat parts rises, so that the hot air in the cooling electronic apparatus is not discharged easily from the air hole of the bottom portion of the casing to the outside. Also, the air warmed with the heat parts is not directly discharged outside the device, and it is therefore considered that the hot air stays easily in the cooling electronic apparatus.
In Document 2, the heat of the CPU provided in a center portion of the note-type personal computer is discharged from an opening of the outside wall of the personal computer with a metal plate (i.e., heat sink) extending to right and left. However, even in this case, the air warmed with the heat parts is not directly discharged outside the note-type personal computer, and therefore the hot air stays easily in the note-type personal computer. Also, in the note-type personal computer, a user requests the slimness thereof (e.g. 2 to 3 cm), and therefore the heat sink connecting between the CPU and the opening of the outside wall of the personal computer may be the best. However, in a device with a height that exceeds 3 cm, it is considered that the hot air stays easily in the device even in the case of the technique of Document 2.
In addition, the heat generated by the heat element is transmitted to the heat sink, the heat sink is warmed, and hence a temperature in the device rises by the heat of the heat sink. It is therefore fear that the rise in temperature has a bad influence on a low heat-resistant element.
For this reason, to discharge the hot air in the device to the outside of the device or improve cooling efficiency of the device by increasing the surface area of the heat sink, the measures to open a plurality of holes to the heat sink are considered. However, when a hole diameter of each hole opened to the heat sink is large, it is considered that the heat conductivity of the heat sink decreases and the dust-proof performance deteriorates. In addition, it is fear that the EMC (ElectroMagnetic Compatibility) performance as the electric performance deteriorates. On the contrary, when the hole diameter of each hole opened to the heat sink is small, a problem that a heat discharge effect and the heat radiation effect are not provided occurs.